Microwave digestion in open vessels has been carried out by others for many years. For instance, in U.S. Pat. No. 4,080,168 to Samra et al. open vessels are used for digestion. Also, in the publication entitled, "Introduction to Microwave Sample Preparation," Kingston et al., American Chemical Society, 1988, a method of open vessel digestion in a microwave oven is described. In such cases the rate of heating and the sample volume were limited by the boiling point of the reagent. Since the walls of the vessels were being heated by the sample, there was no refluxing action to contain the sample and it would spill over if heated too violently.
Most of the subsequent work in this area was directed to microwave systems and vessels for high pressure. For example, U.S. Pat. Nos. 4,904,450 and 5,230,865 to Floyd and Hargett et al. respectively, dealt with the design of vessels and seals for closed vessel microwave digestion at elevated pressures.
In addition, U.S. Pat. No. 5,498,857 to Jacquault does address open vessel digestions. However, in this patent only a portion of each vessel, containing the sample, is enclosed in a microwave application cavity. The remainder of each vessel, which is ambient cooled rather than liquid cooled, is outside the microwave application cavity. Furthermore, the reagent dispensing contained in the system for this patent is also located outside the microwave application cavity. In another U.S. Pat. No. 5,459,302 to Jacquault, a radiation pyrometer is disposed in a chamber of the waveguide directed at one sample which is partially contained within that waveguide.
However, none of the known systems and methods provide both closed and open vessels in one microwave system. The known systems also fail to contain all of the functions within the microwave oven and permit several complete vessels within one microwave cavity. Furthermore, the known systems also do not offer the ability to operate temperature sensing in a microwave oven for controlling the temperature of multiple samples which are totally contained within the microwave oven. It is therefore an object of the present invention to provide a system and method which overcomes the deficiencies of the conventional systems.